Ophthamoscope

ABSTRACT

An ophthalmoscope has illuminating optics ( 10 ) for projecting a beam of light into an eye under examination and imaging optics ( 14 ) for creating an image of said eye for viewing by a user. The imaging optics comprises an objective lens system ( 16 ) and an eye piece lens system ( 20 ). Two corneal reflex stops ( 138  and  148 ) are positioned one on either side of the corneal image formed by the objective lens system. The stops block reflections from the cornea of the eye under examination over a range of distances of the ophthalmoscope from the eye. The use of the two corneal reflex stops results in the precise positioning of the ophthalmoscope relative to the eye under examination not being critical to the blocking of the corneal reflex.

FIELD OF THE INVENTION

This invention relates to ophthalmoscopes.

BACKGROUND TO THE INVENTION

Ophthalmoscopes are instruments used to view the fundus of an eye, andgenerally comprise a light source and a series of optical elements fordirecting illuminating light from the source into an eye underexamination and imaging optics through which the illuminated fundus isviewed. In an indirect ophthalmoscope, a practitioner (or other user)views a real image of the fundus rather than the fundus itself.

A significant amount of the illuminating light beam is reflected fromthe cornea of an eye under examination, and it is important that thesereflections are not seen by the practitioner/user as they will obscurethe view of the fundus under examination. U.S. Pat. No. 3,586,424 showsan ophthalmoscope in which corneal reflexes are blocked by a single stopbetween an objective and an eye piece lens system of the ophthalmoscope.WO 00/30527 shows an ophthalmoscope in which illuminating light isreflected by a reflector within the ophthalmoscope itself towards theophthalmoscope's objective lens systems. The lens system focuses theilluminating light to an apex at the cornea of an eye under examination.The reflector and the apex are substantially conjugate with each otherso that the reflector acts as a stop for the corneal reflex.

However, despite these stops, both types of ophthalmoscope allow somecorneal glare to obscure the viewed image.

SUMMARY OF THE INVENTION

According to the invention, there is provided an ophthalmoscopecomprising illuminating optics for projecting a beam of light into aneye under examination and a housing containing imaging optics forcreating an image of said eye for viewing by a user, the imaging opticscomprising an objective lens system and an eye piece lens system,wherein the ophthalmoscope includes two corneal reflex stops situatedone on either side of the corneal image formed by the objective lenssystem in use, to block reflections from the cornea of the eye underexamination.

Preferably, the ophthalmoscope is an indirect ophthalmoscope.

Preferably, the housing also contains the illumination optics.

The two spaced apart corneal reflex stops are particularly effective atblocking the corneal reflex because the two spaced apart stops to blockthe corneal reflex from patients at varying distances from theophthalmoscope. This flexibility is not provided by prior artophthalmoscopes, in which it is attempted to provide a single cornealreflex stop at the image of the cornea, since the effectiveness of thestop is then highly sensitive to the distance of the patient from theinstrument.

Preferably, each corneal reflex stop has a straight edge, preferablyhorizontal in use, the portion of the stop adjacent to said edgeblocking the reflex. Preferably, the stops each have a part circularaperture, the edge forming a chord of said aperture.

Preferably, the ophthalmoscope includes an inverting lens interposedbetween the objective and eye piece lens systems, the inverting lensbeing operable to cause an erect, non-laterally inverted image of an eyeunder examination to be viewed through the eye piece.

The reflex stops are preferably positioned one on either side of theinverting lens.

Preferably, the two corneal reflex stops are separated by at least 10mm. Preferably, the straight edge of each corneal reflex stop is spaced2 mm from the optical axis of the ophthalmoscope.

Preferably, the ophthalmoscope includes a field stop at the position atwhich the objective lens systems forms an image of the retina of an eyeunder examination.

Such a field stop can be used to reduce glare from light reflected fromthe optical surfaces of the ophthalmoscope, and to reduce the glare fromlight scattered from the non optical surfaces.

The ophthalmoscope may to advantage also include a further field stop,preferably at the position at which the inverting lens forms an image ofthe retina of an eye under examination.

Such a field stop can be used to define the field of view of theophthalmoscope and can further reduce glare from light scattered fromthe non-optical surfaces.

The field stops may to advantage be positioned one on either side of thecorneal reflex stops so that the latter are situated between the fieldstops.

Preferably, the ophthalmoscope includes a front stop, situated in frontof the first said field stop and operable to block lenticular reflexesfrom the eye under examination. In particular, the front stop ispreferably operable to block the fourth Purkinje reflex, i.e. the reflexfrom the rear of the lens of the eye under examination.

Although the fourth Purkinje reflex is of a very low intensity relativeto the corneal reflex, it is bright in relation to the image of theilluminated retina. Certain designs of ophthalmoscope use polarisingfilters to remove the corneal and lenticular reflexes, but in so doingalso filter out potentially useful features from the image of theilluminated retina. The front stop therefore enables the illuminatedretina to be viewed without interference of the fourth Purkinje reflexand without the loss of information which would be caused by polarisers.

Preferably, the illuminating optics are adjustable so as to enable thealignment of the illuminating light with the field viewed through theimaging optics and/or to enable the blocking of the corneal reflex bysaid reflex stops.

Preferably, the illuminating optics comprise a light source verticallyspaced from the imaging optics, and a reflector for reflecting lightfrom the source towards an eye under examination, the reflector beingmovable, preferably by being pivotable about two non-parallel axes toachieve said adjustability.

In this latter case, the reflector is preferably pivotable about avertical axis and a horizontal axis perpendicular to the viewingdirection from the ophthalmoscope to an eye under examination.

Preferably, the reflector is a partial reflector, such as a halfsilvered mirror.

The adjustability of the reflector provides an opportunity (for examplefor the manufacturer) to ensure that the ophthalmoscope is properly setup to illuminate a retina under examination whilst blocking unwantedreflexes.

The illuminating optics may to advantage include a focussing lens whichis movable relative to a light source in a direction lateral to the pathof the illuminating light though the illuminating optics. This enablesthe position of a projected image on the retina of an eye underexamination to be adjusted.

Preferably, the ophthalmoscope illuminating optics include a graticulefor projecting an image onto the eye under examination.

Preferably, the graticule is mounted on a support on which there is alsoprovided at least one stop, the support being movable to bring eitherthe stop or the graticule into registry with the path of theilluminating light through the illuminating optics, to enable image ofthe stop or the graticule either to be projected onto the eye underexamination.

Preferably, the support comprises a rotatable plate.

The reflector may to advantage be situated in front of the objectivelens system. As a result the beam of illuminating light does not passthrough any of the optical elements of the imaging optics before itreaches the eye under examination, thus reducing or avoiding reflectionsfrom those elements.

The ophthalmoscope may include focusing means comprising a control and alinkage connecting the control to a lens means in the viewing system,the linkage comprising a bent flexible rod so arranged that the lens ismoved along the viewing path by non parallel movement of the control.

This provides a very simple, and inexpensive, mechanism linking thecontrol on, for example, a handle of the ophthalmoscope to a lens of theimaging optics.

Preferably said control is slideable.

Preferably said sliding movement of the control is in a directionperpendicular to the viewing direction from the objective lens system toan eye under examination.

For example, the control may be a slider mounted on a handle projectingvertically down from the ophthalmoscope body.

Preferably, the lens means which is connected to the linkage is the eyepiece lens system.

The ophthalmoscope may to advantage provide adjustable magnification ofthe image of an eye under examination, and to that end preferablyincludes two interchangeable inverting lens systems of differingmagnifying powers which are moveable so that either system may be movedinto registry with the objective and eye piece lens system.

Alternatively the adjustable magnification can be achieved by providinga single inverting lens systems which is moveable along the optical axisof the imaging optics.

Thus the user can select the magnification and field of view appropriatefor inspecting the features of interest in a retina under examination,the high magnification being more appropriate for obtaining a moredetailed view of any given localised features, whilst the lowermagnification is potentially advantageous when as much of the retina aspossible needs to be examined in one view.

Preferably, the two interchangeable inverting lens systems are mountedon a common cradle pivotally mounted in the ophthalmoscope so as to bemoveable from one angular position, in which one of the inverting lenssystems is in registry with the objective and eye piece lens systems,into another angular position in which the other inverting lens systemis in registry with the eye piece and objective lens systems, only arespective one of the inverting lens systems being in registry with theobjective and eye piece systems for each of the angular positions of thecradle.

Preferably, the cradle is retained in each of said positions by arespective magnetic fastener.

The ophthalmoscope may to advantage include a rest extending from therear of the eye piece, the rest being operable to control the proximityof the user's eye to the eye piece lens assembly, and being extendibleso that the ophthalmoscope has the same or similar viewingcharacteristics for a user with or without spectacles.

If the practitioner's/user's eye is located significantly away from saidoptimum proximity to the eyepiece lens either forwards or backwardsalong the optical axis then only part of the field of view of theophthalmoscope will be visible. In the extended position the rest isoperable to locate the eye of a user who is not wearing spectacles. Inthe retracted position the rest is operable to locate the eye of a userwho is wearing spectacles.

The imaging optics can therefore provide a full field of view forspectacle wearing and non-spectacle wearing users.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is partially exploded perspective view of an indirectophthalmoscope in accordance with the invention;

FIG. 2 is a sectional side view of the ophthalmoscope with its outercasing removed;

FIG. 3 is an exploded perspective view of the lower portion of theilluminating optics of the ophthalmoscope;

FIG. 4 is an exploded perspective view of part of the imaging optics ofthe ophthalmoscope;

FIG. 5 is a diagram showing the relative positions of the illuminationand viewing paths for the ophthalmoscope;

FIG. 6 is a ray diagram showing the illuminating optics in action;

FIG. 7 is a ray diagram showing the imaging optics in operation.

FIGS. 8( a) and (b) are ray diagrams showing how the corneal reflex froman eye under examination is blocked.

DETAILED DESCRIPTION

With reference to FIG. 1, an ophthalmoscope in accordance with theinvention comprises a housing having two side sections 1 and 2 which aremirror images of each other and a front and top housing section 4 whichextends over the tops of the housing sections 1 and 2 and down the frontof the ophthalmoscope. Each side section has a handle portion 6extending from a main body portion 8. The handle portions 6 extendvertically from the main portion 8, and contains illuminating optics 10for projecting a beam of illuminating light through a window 12 in thefront of the housing section 4. The portion of the housing section 4defining the window 12 constitutes a front stop of the ophthalmoscope.The volume defined by the body portions of the housing sections 1 and 2contains the ophthalmoscope's imaging optics, generally referenced 14.

The imaging optics 14 include an objective lens system 16 from whichlight from an eye under examination passes through either one or twointermediate inverting lens systems in a common cradle 18 to an eyepiece lens system 20 through which a real erect, non-inverted image ofthe retina under examination can be viewed.

The imaging and illuminating optics will now be described.

With reference to FIGS. 1 and 2, the illuminating optics 10 include alower screw threaded connector 22 which surrounds a lamp holder 24 inwhich a halogen light bulb 26 is held in electrical contact with lowerterminals 28 and 30. In use, the screw threaded connector 22 releasablyconnects the bulb to a battery pack (not shown) which is incorporatedinto a handle, supplies power for operating the bulb 26 and whichincludes on-off and brightness controls.

With reference to FIG. 3, the connector 22 forms an integral part of anannular support 32 having a lower flange 34 for acting as a mechanicalstop against which the battery pack abuts, and a concentric connectingtube 36 at the top of which there is provided a focusing lens 38 at aposition coaxial with the filament of the bulb 26. The lens 38 retainedby means of a spring clip 39 located in a lower flange 40 of the member32, which also has a top flange 42 spaced from the flange 40 to define aspace for accommodating a stop and graticule plate 44 sandwiched betweena knurled wheel 46 and a upper filter holder 48.

The wheel 46 forms the outer periphery of a cylindrical member whichincludes an axial spigot (not shown) in registry with slots 50 and 52 inthe graticule/stop plate 44 and the filter holder 48 respectively. Thespigot matingly engages the slots 50 and 52 so that the plate 44 andholder 48 are angularly located relative to the wheel 46 so as to rotatewith the latter.

The underside of the member constituting the wheel 46 is provided with aseries of apertures, for example 54, each in registry with a respectiveformation on the plate 44. Two of those formations are simple apertures56 and 58, each in registry with the respective one of a cobalt bluefilter 60 and a red-free, green filter 62 in the filter holder. Thefilter holder also includes circular apertures, for example, 64, each inregistry with a respective one of the formations in the plate 44.

Turning to the remaining formations on the plate 44, the aperture 66 isa wide angle aperture for illuminating the largest area of the fundus ofthe eye under examination for the best possible diagnosis throughdilated pupils. The aperture 68 is an intermediate aperture whichpermits easier viewing through an undilated pupil in peripheralexamination. This aperture provides illumination which is particularlyuseful in paediatric examination. The aperture 70 is of a smallerdiameter still and is intended for use in illuminating the retina forviewing of the macular area of the fundus or through a small pupil. Theuse of this aperture reduces pupillary reaction and improves patientcomfort. Aperture 72 is a half-moon aperture which provides acombination of depth perception and good field of view whilst aperture74 contains a graticule (shown in detail in FIG. 3A) which is projectedonto the retina to assess the cup/disc ratio as an aid to glaucomadiagnosis and monitoring.

The assembly of the wheel 46, plate 44 and holder 48 is provided with athrough passage through which a spindle pin 78 extends. The pin alsoextends through apertures 80 and 82 in the member 40 and 42 to define anaxis, eccentric with that of the tube 36, about which the assemblyrotates. It will be appreciated that a user can select which of theformations on the plate 44 and/or which the filters 60 and 62 is to bein registry with the path of light from the bulb 26, and thereby selectsa mode of operation of the ophthalmoscope from a number of possiblealternatives.

The upper flange 42 of the holder has a central aperture whichaccommodates a relay lens holder 84 for a relay lens 86 held in positionin the holder 84 by means of by a spring clip 88. At the top of theholder 84 there is provided an infrared filter 90. The top of the flange42 is also formed with a slot 92 running along a chord of the flange 42,and accommodating a leaf spring 94 which acts against the holder 84 tourge it against one side of the circular portion of the aperture in theflange 42.

That aperture is of a larger diameter than that of the holder 84 so thatthe holder 84 may move along either of two horizontal perpendicular axesrelative to the flange 42. The flange 42 includes a pair of radial screwthreaded through bores, each of which accommodates a respective one oftwo grub screws 96 and 98. These screws act against the periphery of thelens holder 84, against the action of the spring 94, and enable theposition of the lens 86 to be laterally adjusted, to achieve alignmentof the illuminating light with the field viewed through the imagingoptics 14.

A mirror 100 is positioned above the filter 90 and reflects light fromthe bulb 26 forwards and downwards onto a further angled mirror 102,which, in turn, reflects the light up through a projection lens system104 onto an angled partially reflecting mirror 106. The mirror 106 ismounted on a turntable 108 which may rotate about a vertical axispassing through the centre of the mirror 106. The mirror is mounted onthe turntable 108 by means of two vertical posts 110 and 112 on whichthe mirror is pivotably mounted so as to pivot about a horizontal axiswhich passes through the centre of the mirrors reflective surface and isin the plane of the latter. A light trap in the form of a matt blacksurface on the underside of the ophthalmoscope housing is situatedimmediately above the mirror 106 so as to trap any stray light passingthere through from the mirror 102. The light that is reflected forwardsto the mirror 106 passes through the window 12 and into the eye underexamination.

In use, the mirror 106 is so orientated relative to the rest of theophthalmoscope that the corneal reflex is blocked by the corneal reflexstops 138 and 148 shown in FIG. 4. The fourth Purkinje reflex is blockedby the front stop. Light from the eye under examination passes backthrough the window 12 and through the half silvered mirror 106 into theobjective lens system 16. The lens system 16 is mounted in a cylindricalholder 114 and comprises two lenses. The holder 114 also contains acylindrical insert 116 which is of a smaller internal diameter than thatof holder 114 which positions a 12.4 mm diameter field stop 118 at 24.30mm from the inner lens of the objective lens system 16. The underside ofthe holder 114 also carries mirror 100 and its holder.

The end of the holder 114 remote from the lens system 16 includes threesockets which are equiangularly spaced around the holder 14 and each ofwhich accommodates an end of a respective rigid rod which extends to aneye piece holder 120 (which has corresponding sockets for the other endsof the rods) to fix the two holders relative to each other. In betweenthe two holders 114 and 120 there is provided the cradle 18 shown inmore detail in FIG. 4.

The cradle 18 has a lower portion 122 which defines two upwardly facingpart cylindrical channels 124 and 126, each of which accommodates arespective one of two cylindrical holders 128 and 130 held in positionby a cap 132 which is screwed (by screw 134) onto the portion 122 of thecradle.

Two of the rods are shown at 117 and 119 in FIG. 1.

The holder 130 has a machined step against which lens 144 and 142 abut.Wire clip 146 keeps lens 144 abutted with the machined step.

A corneal reflex stop 148 in the form of a ring shaped member having agenerally D-shaped aperture, the top of which defines the lower straightedge of the stop, is located with a tab that extends verticallydownwards from the outer edge and engages a corresponding slot in theholder 130 and abuts clip 146. Wire clip 150 abuts stop 148. Stop 138abuts lens 142 and its tab locates in similar fashion to stop 148. Wireclip 136 abuts stop 138. Tabs on stop 138/stop 148 align with locationpin in body of 130 to ensure correct alignment of stops in imagingoptics. Locations pins in bodies 130 and 128 locate in slots in lowerportion of part cylindrical channel 124 and 126.

The contents of the holder 128 are identical to those of the holder 130,save for the lenses which have a different power so that the invertinglens system in the holder 128 has different magnification from thatprovided by the lenses in the holder 130.

The forward portion of the cradle 18 includes a through bore 152 inregistry with an aperture 154 in a rear lug on the underside of thecradle 18. A pivot 156 extends through the bore 152 and the aperture 154so that the cradle 18 can pivot about the pin 156. The rearward end ofthe pin 156 includes a screw threaded connector 160 Which extends into acorresponding aperture 158 in the eye piece holder 120.

The cradle includes through a passage 162 immediately above the bore 152and a lug defining an aperture 154 for accommodating the rod 119 whichpasses through the lower portion of the cradle with enough clearance toenable the cradle to assume either of two operating angular positions.The cradle also has a magnet 164 fixed in a recess 166 in one side ofthe cradle. A similar magnet and recess are provided on the oppositeside. The magnets co-operate with ferromagnetic rod 119 to hold thecradle in either of its two angular positions. A control 168 extendsfrom the bottom of the cradle 18 from the other side of the pivot axisdefined by the pin 156 so that manipulation of the control 168 rocks thecradle 18 into either of its two angular operating positions.

In one of those operating positions, the holder 130 is in registry withthe viewing path of the imaging optics, the holder 128 being clear ofthe viewing path, whilst in the other position the situation isreversed, i.e. the holder 130 is clear of the viewing path whilst theholder 128 is registry with the end path.

The eye piece holder 120 has a forward cylindrical passage 170 (FIG. 2)separated from a rear passage 172 by an annular shoulder 174.

The shoulder 174 constitutes the eye piece field stop which is of adiameter of 5.3 mm, and which helps to cut down glare from reflectionsfrom the optical surfaces of the ophthalmoscope and reduces glare due tolight scattered from the non-optical surfaces. The stop in shoulder 174is at the infinity focus of the objective and inverting lens systems.

The eye piece lens systems comprises an achromatic doublet 176 and afurther lens 178 separated from each other by a spacer ring 180 and heldin position in a cylindrical eye piece lens holder 182 by a spring clip184.

In the top of the holder 182 there is provided a screw threaded bore 186which is in registry with a top slot 188 in the eye piece holder 120.

A screw 189 extends through the slot 188 and into the bore 186 so as toattach a flexible strip 190 to the eye piece lens holder 182.

The strip 190 curves through 90° and is terminated at a control slider192. The strip includes a central elongate aperture 194 (FIG. 1) so thatit does not obscure the viewing path.

The strip is flexible so that vertical movement of the slider 192 istransmitted by the strip to the eye piece lens holder 182 to causehorizontal movement of the latter. The strip 190 thus acts as a flexibleconnecting rod between the control slider 192 and the eye piece lenssystem, so as to provide a focusing control for the ophthalmoscope. Theophthalmoscope also includes a slideable rear cylindrical casing portion196 which is slideably mounted in the ophthalmoscope housing and ismovable from an extended position, as shown in FIG. 2, to a retractedposition in which the outboard end of the portion 196 is adjacent to theeye piece lens system. If the user is wearing spectacles, the portion isto be placed in its retracted condition, whereas the extended positionwould be used by a user who is not wearing spectacles. Thus the distanceof the eye of the user from the eye piece lens system remains the same,whether or not the user is wearing spectacles.

In use, the user selects a suitable brightness level for the halogenbulb 26 (using controls on the battery casing). The user also selectsthe appropriate inverting lens system using the control 168.

The lens system contained in the holder 128 causes the ophthalmoscope tohave a field of view of 17.5° and magnification of 1.5 (corresponding toa retinal magnification of 22.5), whilst the inverting lens systemcontained in the holder 130 causes the ophthalmoscope to have a 25°field of view and a magnification of 1.0 (retinal magnification of 15).

The distance between corneal stops in the holder 128 is 11.5 mm (plus orminus 1 mm) whilst that of the stops in the holder 130 is 13.9 mm (plusor minus 1 mm). Various other distances between the optical elements inthe imaging optics are shown in FIG. 7.

As can be seen from FIG. 5, the illuminating beam axis 206 extends, inuse vertically upwards from the mirror 102 to intersect the mirror 106at a position 0.7 mm vertically beneath the point at which the axis(208) of the eye under examination intersects the mirror 106. Theoptical axis 218 of the viewing system intersects the front of themirror 106 at a position 1 mm vertically above the point of intersectionof the eye axis, so that the illumination and viewing axis are spacedfrom each other by 1.7 mm. The refraction caused by the mirror 106 onthe light passing through it to the imaging optics increased thevertical distance between the viewing and illumination axes to 2.03 mm.

The operation of the ophthalmoscope will now be described.

Initially the user looks at the patients eye through the ophthalmoscopefrom some distance away from the patient's eye so that the user can seethe patient's pupil and centre it in the field of view. Then byadjusting the angle of the ophthalmoscope the user can view a small partof the retina through the pupil. This partial view is seen as a redpatch. The user then moves towards the patient maintaining the view ofthe retina. As the user gets closer to the patient more and more of theretina can be seen. At some point the corneal reflex becomes obviousand, if not blocked, will be so bright that the retinal image can belonger be seen. At this point the angle of the ophthalmoscope isadjusted to ‘move’ the reflex behind the front reflex stop. This is thecondition shown in FIG. 8( a) where the front reflex stop 138 completelyblocks the corneal reflex. At this point a large area of the retina canbe seen but the user has to move even closer to acquire the fullavailable view. As the user moves closer the front reflex stop is lesseffective. The rear reflex stop 148 now blocks that part of the reflexwhich is not blocked by the front reflex stop. The two stops workingtogether enable the reflex to be completely blocked down to, and beyond,the point at which the full field-of-view can be seen as shown in FIG.8( b).

FIG. 8( a) shows the fan of rays 200 which, but for the stop 138, couldreflect off the cornea and be transmitted through to the practitioner'seye giving a strong corneal reflex (much stronger than the retinalimage). These rays are, however, completely blocked by the front reflexstop 138. Note that only rays through the rear half of the relay lenscan contribute to a corneal reflex; rays through the front half of thelens are reflected outside the field of view by the cornea.

FIG. 8( b) shows that a complete fan of rays 202 could contribute to areflex, if the ophthalmoscope is moved closer to the patients eye. Inthis situation however, the rays are completely blocked by one or otherof the two reflex stops 138, 148.

The reflex stops are especially effective because

-   -   i) they are positioned close to the image of the cornea produced        by the objective lens system 16.        and/or    -   ii) the illumination system is designed to project a small image        of the filament near to the cornea.

Ideally the filament would be imaged at the cornea but this is notconsistent with projecting the maximum amount of light onto the retina.This latter condition is achieved by imaging the filament onto thepatient's pupil—some 3 mm distant behind the cornea. The compromise isto project the filament image to be between the pupil and the cornea.

The image of the cornea is in the centre of the inverting lens system142, 144 and it would be difficult to place a stop here. The compromisehas been to put stops on either side of these lenses. This has had theconsiderable advantage of increasing the range of distance between theophthalmoscope and patient over which the corneal reflex can beeffectively blocked.

1. An ophthalmoscope comprising illuminating optics for projecting abeam of light into an eye under examination and a housing containingimaging optics for creating an image of said eye for viewing by a user,the imaging optics comprising an objective lens system and an eye piecelens system, wherein the ophthalmoscope includes two corneal reflexstops situated one on either side of the corneal image formed by theobjective lens system in use, to block reflections from the cornea ofthe eye under examination.
 2. An ophthalmoscope according to claim 1, inwhich the ophthalmoscope is an indirect ophthalmoscope.
 3. Anophthalmoscope according to claim 1 in which the housing also containsthe illuminating optics.
 4. An ophthalmoscope according to claim 1, inwhich each corneal reflex stop has a straight edge, the portion of thestop adjacent to said edge blocking the reflex.
 5. An ophthalmoscopeaccording to claim 4, in which each said straight edge is horizontal inuse.
 6. An ophthalmoscope according to claim 4, in which the stops eachhave a part circular aperture, the edge forming a chord of saidaperture.
 7. An ophthalmoscope according to claim 4, in which thestraight edge of each corneal reflex stop is spaced 2 mm from theoptical axis of the ophthalmoscope.
 8. An ophthalmoscope according toclaim 1, in which the ophthalmoscope includes an inverting lensinterposed between the objective and eye piece lens systems, theinverting lens being operable to cause an erect, non-laterally invertedimage of an eye under examination to be viewed through the eye piece. 9.An ophthalmoscope according to claim 8, in which the reflex stops arepositioned one on either side of the inverting lens.
 10. Anophthalmoscope according to claim 8, in which the ophthalmoscopeincludes a field stop at the position at which the objective lenssystems forms an image of the retina of an eye under examination.
 11. Anophthalmoscope according to claim 10, in which the ophthalmoscopeincludes a further field stop.
 12. An ophthalmoscope according to claim11, in which said further field stop is at the position at which theinverting lens forms an image of the retina of an eye under examination.13. An ophthalmoscope according to claim 10, in which the field stopsare positioned one on either side of the corneal reflex stops so thatthe latter are situated between the field stops.
 14. An ophthalmoscopeaccording to claim 10, in which the ophthalmoscope includes a frontstop, situated in front of the first said field stop operable to blocklenticular reflexes from the eye under examination.
 15. Anophthalmoscope according to claim 14, in which the front stop isoperable to block the fourth Purkinje reflex.
 16. An ophthalmoscopeaccording to claim 1, in which the two corneal reflex stops areseparated by at least 10 mm.
 17. An ophthalmoscope according to claim 1,in which the illuminating optics are adjustable so as to enable thealignment of the illuminating light with the field viewed through theimaging optics and/or to enable the blocking of the corneal reflex bysaid reflex stops.
 18. An ophthalmoscope according to claim 17, in whichthe illuminating optics comprise a light source vertically spaced fromthe imaging optics, and a reflector for reflecting light from the sourcetowards an eye under examination, the reflector being movable to achievesaid adjustability.
 19. An ophthalmoscope according to claim 18, inwhich the reflector is pivotable about a vertical axis and a horizontalaxis perpendicular to the viewing direction from the ophthalmoscope toan eye under examination.
 20. An ophthalmoscope according to claim 19,in which reflector is a partial reflector.
 21. An ophthalmoscopeaccording to claim 17, in which the reflector is situated in front ofthe objective lens system.
 22. An ophthalmoscope according to claim 17,in which the illuminating optics include a focussing lens which ismovable relative to a light source in a direction lateral to the path ofthe illuminating light though the illuminating optics.
 23. Anophthalmoscope according to claim 1, in which the illuminating opticsinclude a graticule for projecting an image onto the eye underexamination.
 24. An ophthalmoscope according to claim 23, in which thegraticule is mounted on a support on which there is also provided atleast one stop, the support being movable to bring either the stop orthe graticule into registry with the path of the illuminating lightthrough the illuminating optics, to enable image of the stop or thegraticule either to be projected onto the eye under examination.
 25. Anophthalmoscope according to claim 24, in which the support comprises arotatable plate.
 26. An ophthalmoscope according to claim 1, in whichthe ophthalmoscope includes focusing means comprising a control and alinkage connecting the control to a lens means in the imaging optics,the linkage comprising a bent flexible rod so arranged that the lensmeans is moved along the viewing path by non parallel movement of thecontrol.
 27. An ophthalmoscope according to claim 26 in which saidcontrol is slideable.
 28. An ophthalmoscope according to claim 27, inwhich said sliding movement of the control is in a directionperpendicular to the viewing direction from the objective lens system toan eye under examination.
 29. An ophthalmoscope according to claim 26,in which the lens means which is connected to the linkage is the eyepiece lens system.
 30. An ophthalmoscope according to claim 1, in whichthe ophthalmoscope provides adjustable magnification of the image of aneye under examination.
 31. An ophthalmoscope according to claim 30, inwhich said adjustable magnification is achieved by means of twointerchangeable inverting lens systems of differing magnifying powerswhich are moveable so that either system may be moved into registry withthe objective and eye piece lens system.
 32. An ophthalmoscope accordingto claim 31, in which the two interchangeable inverting lens systems aremounted on a common cradle pivotally mounted in the ophthalmoscope so asto be moveable from one angular position, in which one of the invertinglens systems is in registry with the objective and eye piece lenssystems, into another angular position in which the other inverting lenssystem is in registry with the eye piece and objective lens systems,only a respective one of the inverting lens systems being in registrywith the objective and eye piece systems for each of the angularpositions of the cradle.
 33. An ophthalmoscope according to claim 32, inwhich the cradle is retained in each of said positions by one or moremagnetic fasteners.
 34. An ophthalmoscope according to claim 1, in whichthe ophthalmoscope includes a rest extending from the rear of the eyepiece, the rest being operable to control the proximity of the user'seye to the eye piece lens assembly, and being extendible so that theophthalmoscope has the same or similar viewing characteristics for auser with or without spectacles.